Printer&#39;s blanket



Patented July 11, 1939 PATENT OFFICE PRINTERS BLANKET Raymond E. Thomas, Newburgh, N. Y., assignor to E. I. du Pont de Nemoursv & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application December 17, 1937, Serial N0. 180,327

3 Claims.

This invention relates to feltlike fabrics impregnated with cellulose derivatives, and more particularly to printers blankets and the like made of woven felts impregnated and coated with cellulose nitrate.

In many rotary printing presses, for example those used in printing newspapers, the printing unit consists essentially of two rotary cylinders, one for carrying the type (called the plate cylinder), and the other for pressing the sheet to be printed against the type on the plate cylinder (called the impression cylinder). The printing elements (type) on the plate cylinder frequently have surface irregularities (for example some type faces above or below the general printing surface level). It is common practice to provide the impression cylinder (which is usually made of some hard, unyielding material such as metal) with a resilient surface to compensate for such unevenness. In this way an even printing impression over the entire surface of the sheet being printed may be obtained. Such a resilient surface is ordinarily obtained by covering the cylinder face with a replaceable blanket. These coverings or blankets must, in addition to being resilient, be non-penetrable by printing inks and ink removers, and possessed of a hard, noncracking, non-peeling, flexible surface capable of withstanding millions of pressure applications of great magnitude (by the plate cylinders).

I his problem has attracted many investigators. In spite of the many proposed sc utions, among which may be mentioned those of United States Patents Numbers 660,752, 729,683, 1,096,896, 1,147,942, 1,158,033, 1,231,141, 1,231,142, 1,237,493, 1,311,596, 1,492,123, 1,702,620, 2,011,248, and 2,076,376, no satisfactory blanket has been devised (see review of the situation in U. S. P. 1,983,352). The nearest approach to a satisfactory blanket offered commercially so far has been expensive and difiicult to produce. The coated felt type (U. S. P. 1,855,798) has features to recommend it, but the ready detachment of the coating from the base after short use has caused the composition type (U. S. P. 1,464,242) to be widely used.

This invention had for an object the provision of a cellulosederivative impregnated woven felt fabric. Another object was the production of a firm, resilient, printer's blanket base capable of being strongly bonded with a surface coating. Still further objects were to produce a wear-resistant printers blanket having a satisfactorily bonded surface coating which was hard but flex- 5 ible; to produce a printers blanket non-penetrable by inks, moisture and cleansing solvents (such as hydrocarbons, carbon tetrachloride, and the like); to produce a press blanket the base of which is an impregnated relatively thick woven felted wool fabric sufficiently firm in texture to prevent spreading and stretching but resilient enought to give a satisfactory cushioning effect and to satisfactorily support a surface coating; to devise methods of making the aforementioned products; and to prepare improved coatings for printers blankets. An additional specific object was the preparation of a dry, hard, flexible, resilient, non-cracking, non-peeling, non-tacky, coated, impregnated woven felted Wool base printers press blanket resistant to printing inks and ink removers (cleansing solvents) and capable of withstanding repeated pressure applications of great magnitude. A general advance in the art and other objects which will appear hereinafter are also contemplated.

It has now been found that a printers blanket having the aforementioned desirable characteristics may be produced by impregnating a woven felt fabric with a cellulose derivative aqueous emulsion of the oil ,in water type, and thereafter coating the base thus formed with a cellulose derivative composition. In this way a felt fabric having increased and satisfactory firmness and resiliency and a desirably anchored (bonded) coating is produced. Surprising as it may seem,

the bond between the base and coating is stronger and more lasting in a press blanket produced in this manner, and the product has superior hardness, flexibility and resistance to crackng and peeling.

From the following description and specific examples, in which are disclosed certain embodiments of the invention as well as details of what is believed to be the best mode for carrying out the invention, it will be apparent how the foregoing objects and relatedends are accomplished. The quantities are given in parts by weight throughout the application. 5

In carrying out the invention a feltlike base of high tensile strength, uniformity homogeneity and resiliency, and characterized by rapid return to its original thickness after being compressed, is constructed in the manner set out in the following Paragraphs.

A high grade wool is selected and carded inthe usual manner. and spun on spinning machines, the warp yarns being given a tighter twist than the filling yarns. The spun yarns are then woven into a single ply fabric with a single cross weave. Care is taken to avoid weaving the yarns too tightly, since a tight weave hinders subsequent felting and does not venable the fabric to be built up to as great a thickness as is possible with loosely woven yarns.

The woven fabric is then felted by a fulling process. This is conveniently carried out by forming the woven felt into a continuous belt and passing it through a soap solution inan apparatus similar to a jig. The type of fulling apparatus determines the length of the belt. The width of the belt will vary (at the start) according to the apparatus and woven stock available. During the fulling process the continuously until no further change in the dimensions of the fabric can be observed, at which point the fulling operation is considered finished. In general complete fulling of a fabric of this character produces a reduction in length of 25% to 35% and a reduction in width from 40% to 50%. In one specific instance a piece of fabric approximately 110 yards long and '72 inches wide was continuously passed through a soap solution for about 14 hours. It was then found to have diminished in length to approximately yards and in width to approximately 38 inches.

After the fulling operation the fabric is washed free from soap and dried in a tenter frame under little or no tension. The fabric is (preferably) dried in a horizontal position and without applying enough tension thereto to stretch it beyond its minimum width while in thewetted state.

After the fulled fabric has been washed and dried the heavy surface fibers are sheared off on both sides. It is then sanded and again sheared. The sanding operation may be satisfactorily carried outby a revolving cylinder covered with garnet paper or sandpaper. The fibers are thereafter sheared very close to produce a pile finish.

Since the felt at this stage is not firm, compact or dense enough to meet the conditions of present day printing practice, it is compressed to the desired extent by passing between calender rolls. The thickness of the resulting product may be used as a gauge. The felt is then impregnated with a sizing composition in order that it may not lose its compact condition. The sizing compov sitions used according to this invention are new, and in addition to holding the felt in a compressed and compact state, enable a cellulose derivative surface coating to be anchored to the base in a superior manner.

A particularly desirable impregnating compo: sition is an aqueous cellulose nitrate oil in water type emulsion. A typical emulsion may be prepared in the following manner. A cellulose nitrate colloid, for convenience called colloid A,

and havin the composition:

The carded wool roping is drawn fabric diminishes in' length and width. The process is carried out is prepared and mixed with a gum colloid, for convenience called colloid B, having the composition:

Ewample II Sodium benzoate .005 Soluble ghatti gum .500 Soluble soap DDW .200 Water (lukewarm) 14.495 15.2%

The resultant emulsion is diluted with 25% of its weight of water before being used for impregnation.

The cellulose nitrate in colloid A has a nitro- 'gen content of 11.35% to'11.75% and a viscosity characteristic of 12.0 to 20.0 seconds as determined by A. S. T. M. 'D-301-33.

This viscosity characteristic is the time required for a T g inch steel sphere to fall 10 inches through a solution consisting of:

Per cent Cellulose nitrate 12.2 Denatured alcohol (Z-B formula) 22.0 Tnlnnl 48.3 Ethyl acetate 17.5

The denatured alcohol used in the above formulation is that corresponding to Internal Revenue'Bureau formulaZ-B denatured alcohol which consists of 100 gallons of by volume of ethyl alcohol to which is added one-half gallon of benzol.

The soluble soap DDW is a substantially dry mixture of the sodium salts of the sulfates of the mixture of alcohols obtained by hydrogenation of coconut oil acids (see Journal of Society of Dyers and Colorists 1932, volume. 48, page 129). Such alcohols are of the straight chain type, and the major constituent has 12 carbon atoms.

In preparing the emulsion, the sodium benzoate, soluble soap DDW, and soluble ghatti gum (ingredients of colloid B) were added to the lukewarm water and stirred, rapidly until dissolved. After solution was complete colloid A was slowly added with rapid stirring. To insure complete emulsification the stirring is continued for from four to five minutes after all of colloid A had 1 been added to colloid B. I

I ner.

The impregnation of the felt is carried out with the thus prepared emulsion in any suitable impregnating equipment, such as, for example,

a mangle, in which case the felt passes'through squeeze rolls each time it goes through the impregnating bath. The felt is given three ends through the impregnating bath. During the impregnating of the felt, approximately 32.5 parts of the felt absorbs approximately 67.5 parts of the sizing composition. Approximately 9.0% of the weight of the finished felt consists of the solid components from the impregnating bath.

After the felt is impregnated with the cellulose nitrate emulsion, it is dried in a tenter frame under substantially no tension. The dry impregnated felt is passed through a calender to obtain the desired thickness or density. For most purposes, the impregnated felt after pressing should have a thickness of not less than .056 inch and not more than .090 inch. In some cases it is necessaryto submit the impregnated felt to several pressure applications to obtain the desired thickness or density.

When the impregnated felt prepared in the above described manner is to be made into a coated press blanket, it is provided with a noncracking, non-peeling, ink resistant flexible coating utilizing a cellulose derivative as the film forming constituent. In the preferred embodiment this coating consists of. an inner portion comprising essentially cellulose nitrate (this por-. tion ordinarily contains a small amount of plasticizer) an intermediate portion comprising essentially cellulose nitrate together with pigment and plasticizer and an outer portion comprising essentially cellulose nitrate and an ink repellent material such as aluminum bronze or its equivalent.

Typical .inner coating compositions are:

Example III The cellulose nitrate of these examples has a nitrogen content of 12.3% to 12.5% and a viscosity of to seconds (determined by the A. S. T. M. D-301-33 method).

The Paraplex RG-2 Resin is a castor oil modified glycerol sebacate mixed with two-thirds its weight of toluene. It is a product well known in commerce, being available in the open market. The corresponding plasticizer produced from diethylene glycol instead of glycerol gives substantially identical results both in the above example and inthe other examples of the specification.

It is possible to obtain a slightly better bond between the flexible coating and the impregnated felt by the composition of Example III, but its use results in a sacrifice of suppleness. Very desirable suppleness is obtained with a small amount of plasticizer, as shown in Example IV.

Generally two coats of the inner" coating composition are applied to the .impregnated felt by means of a doctor knife. In this way approximately 12 ounces of non-volatile' material are deposited per square yard. After each coat the treated felt is passed through a heated drying tunnel to expel the volatile components of the coating material.

After the inner.coating is completed, a plurality of coats of an intermediate coating composition are applied.

A typical intermediate coating composition 15:

Example V Per cent Mill base 12.1. 24 ounce cellulose nitrate solution (24 ounces C. N. for each gallon of solvent) in 60-40 ethyl alcohol-ethyl acetate (17.44% C. N. by weight) 50.4 Paraplex RG-Z Resin 17.1 Ethyl alcohol 12.2 Ethyl acetate 8.2

Example VI Per cent Lithopone 36.10 Yellow ochre 12.04 Bone black 6.26 Paraplex RG-2 Resin 45.60

after the substances listed have been dispersed in a ball mill and each individual pigment particle has been wetted. This grinding usually requires about 8 hours. This dispersing of the pigment in the resin-like material gives a composition especially adapted for mixing with the cellulose nitrate solution mixture. 7

According to the preferred procedure, immediately following the application of the two coats of the inner coating composition there is applied one coat of the above intermediate coating composition (by means of a doctor knife) and the volatile solvents thereof expelled (by passing the coated material through a heated chamber).

The thus treated material is then passed between embossing or calender rolls to further improve the anchorage of the coating to the felt base and to smooth out any unevenness in the coated surface. Following this first calendering, approximately 18 coats of the intermediate coating composition are applied. The volatile constituents are expelled after each coating operation. A

calendering operation similar to that mentioned above is carried out after every sixth coat. In this way there is applied approximately 42 ounces of coating material per square yard from the "intermediate coating composition.

It is usually necessary to finish the blanket within a definite thickness. A customary tolerance is .001 inch. For this reason the amount of coating varies, depending upon the thickness of the felt before coating.

Following the application of the final coat of the plasticized, pigmented intermediate coating composition, the coated surface is sprayed with a low concentration surface'lacquer containing aluminum particles or flakes. This outer surface lacquer (coating composition) is preferably:

Example VII Percent 24 oz. cellulose nitrate solution 24.4 Butyl acetate 29.3 Ethyl alcohol 13.31 Ethyl acetate 29.30 Flat aluminum particles or flakes 3.69

The cellulose nitrate in the above formula is the same as that described in ExampleIV.

cient lacquer to completely cover the fintermediate coating, the material is finished and is ready for use.

The amount of coating deposited is controlled" in order that the finished product ,will have a definite thickness, Following is a list of different thicknesses of felt before coating, and the preferred thickness of the finished product.

While the specific embodiments have disclosed the woven felted fabric as a woolen felt, other textile woven fabrics, such as cotton, may in some cases be used. It is believed that woolen fabrics are best suited for the purposes of the present invention, and, therefore,,woolen feltedfabric are preferred. The fabric may be single ply with a single cross-weave, double cross-weave or any other type weave commonly used for weaving felt sheets or fabrics. The yarn may also be woven into a multi-ply fabric -in which case the separate plies are suitably bound together by binder warps. Any type of weave -or felting of the woven felted fabric yielding a product of requisite properties may be used in carrying out the invention.

The new impregnating (sizing) composition disclosed above holds the compressed felt in a compact condition and provides an improved means for securing or bonding the surface coat- In addition, the sizing composition adds body or firmness to the felt, which aids it in retaining the resilient condition to which it is brought by the pressing operation. The sizing composition also tends to hold the fibers together and prevent them from springing apart when subjected to repeated pressure of great magnitude.

While the most desirable concentration of the sizing composition is obtained by diluting the emulsion produced by mixing colloid A and colcomplete emulsion.

loid B of the specific example with one part of water to four parts of said emulsion, other consistencies, for example the range from no water up to one part of water to one part of emulsion may be satisfactorily employed. The undiluted emulsion, which hasa consistency slightly greater than water, may be prepared and stored for an indefinite period of time prior to its use. It is desirable to dilutethe emulsion just prior to use .in order to cut down on storage space.

For the impregnating step, in order to insure thorough impregnation it is preferred to employ an emulsion in which the internal phase is of low viscosity, and the emulsion of the specific example has proved exceptionally satisfactory However, higher viscosity dispersed phases may be used in the emulsion at the sacrifice of penetration of the emulsion throughout the woven ,f'fabric. The penetrating propertiesof the emul- After spraying the coated surfacewith, sufiision depend primarily upon the viscosity of the dispersed phase rather than the viscosity of the It is possible to eliminate the water in colloid A and still obtain a satisfactory impregnating emulsion. Water is present in the preferred example primarily for economic reasons because cellulose nitrate (as is Well known) is shipped either alcohol or water wet. Inasmuch as alcohol is an introfier (dispersible in both phases of an emulsion), in this type of emulsion it cannot be used to any appreciable extent. Cellulose nitrate which is water wet and not alcohol wet is therefore commonly employed. Instead of cellulose nitrate, other cellulose derivatives which are capable of being emulsified may be substituted in colloid A. Among these may be mentioned ethyl cellulose, benzyl cellulose, cellulose acetobutyrate, cellulose formate, cellulose acetate and cellulose .propionate. It is also within the scope of the invention to employ mixtures of cellulose derivatives, for example cellulose acetate and cellulose nitrate, in colloid A.

The gasoline in colloid A can be replaced by any pyroxylin diluent or solvent, either aromatic or aliphatic, whichis substantially incompatible with water, for example, xylene, toluene,

benzene and straight chain hydrocarbons.

In the preferred formula, tertiary amyl alcohol is present as a diluent to reduce 'the viscosity of colloid A. It accomplishes this without excess dilution. Other high boiling alcohols substantially incompatible with water may be used, for example, butyl, amyl, etc.

The butyl acetate in colloid A may be replaced by any pyroxylin solvent which is substantially incompatible with water and boils at a temperature sufficiently high so that the water will evaporate before the solvent; for the pyroxylin evaporates.

Sodium benzoate is present in the preferred emulsion formula as a preservative for the soluble ghatti gum. Other well known preservatives may be used for this purpose.

The soluble ghatti gum is the bodying agent for the colloid B and the soluble soap DDW is a surface tension reducer for the water present in the emulsion. The soluble ghatti gum and soluble soap DDW combined behave as the emulsifying agent. The ghatti gum may be replaced by similar materials, such for example as gelatin, casein, glue or gluten. The soluble soap DDW may be replaced by other soluble soaps generally used as emulsifying agents, for example,

potassium and sodium soaps of ricinoleic,linoleic and o1eic acid.

Example VIII Percent A:

Cellulose nitrate 5.0 Water 9.8 Castor oil 10.0 Tertiary amyl alcohol- 15.0 Butyl acetate 45.0

Colloid B:

Soluble ghattigum. .500 Sodium benzoate .005 Lukewarm water 14.495 Soluble soap DDW .200

Example IX Colloid A:

Cellulose nitrate 5.0 Water 9.8 Dibutyl phthalate 2.5 Tertiary amyl alcohol 17.5 Butyl acetate L 45.0 Gasoline; 5.0 40 Colloid B:

Soluble ghatti gum .500 Sodium benzoate .005 Lukewarm water 14.495 Soluble soap DDW .200

Example X Colloid A:

Cellulose nitrate 5.0 Water 9.8 Tricresyl phosphate 5.0 Butyl acetate 20.0 Colloid B:

Gelatin glue 3.0 Lukewarm water 57.0 Soluble soap DDW .2

appreciable range, depending upon the viscosity of the pyroxylin, solvents, diluents, etc.

The pliability or degree of stiffness of felts may be regulated by impregnation with aqueous cellulose derivative emulsions formulated to accomplish the desired result.

When additional softness or increased suppleness of the felt is desired, a softener for the pyroxylin may be employed in colloid A of the emulsion, the degree of stiffness decreasing with an increase in plasticizer content. Emulsions of this type are disclosed in Examples VIII, IX and When suppleness and reduced stiffness in the felt are especially important, an emulsion is prepared in which the pyroxylin solvent boils below the boiling point of water. This type of emulsion is disclosed in Example Xi as follows:

Example XI L Percent Colloid A:

Cellulose nitrate 15.0 Water 7.5 Ethyl acetate 52.5 Colloid B:

Soluble ghatti gum .5 Soluble soap DDW l .2 Water 24.3 Felts prepared from such compositions are supple and are not ,stifiened to any substantial degree.

Although it is not desired to limit the patent to any particular theory, the following is offered to aid in understanding the invention. It seems probable that after evaporation of the volatile constituents of the impregnating composition the cellulose nitrate is distributed throughout the felt base in the form of small particles. When water and organic liquids having higher boiling points, such as amyl alcohol and butyl acetate, are utilized, there is a tendency for the precipitated particles to coalesce and form a body having a certain degree of continuity. This tendency is not apparent when water is used in connection with the cellulose nitrate suspension media which are volatile below the boiling point of water, for example, ethyl acetate. Secure anchoring of the surface film of cellulose nitrate to the base is made possible by means of the cellulose nitrate in the felt precipitated in the manner described. A slight stiffening of the felt has been noticed when, in the drying operation, the non-solvent (non-solvent for cellulose nitrate) materials are driven off before the last of the organic liquids having a solvent action on the cellulose nitrate.

While the invention in its most specific aspect is for a printer's blanket and a process of making the same, the impregnated felt is a distinct advance in the art and finds utility in the textile industry for materials other than printers blankets. The aqueous cellulose derivative emulsion may be used as a bodying agent for all types of felts. The aqueous cellulose derivative emulsion may also be used for the impregnation of woven textiles, e. g., drills, sateens, broken twills,-

etc., which may or may not be further treated by a surface coating of a film forming composition.

Aqueous cellulose derivative emulsions penetrate much further into the felt than a dispersion of cellulose derivatives in organic solvents having the same percentage solids as the emulsion would. Contradictory as it appears, one result of the deeper penetration of the emulsion into the body of the felt is an increase in resiliency. This causes a printers blanket made by the herein described process to have a superior cushioning efiect when a high spot in the type presses on the paper supported by the blanket, and results in a more evenly printed surface than has heretofore been possible. A further outstanding advantage of the impregnation with the aqueous cellulose derivative emulsion is a marked advantage in the strength of the bond between the impregnated felt and the surface coating thereon. Because of this strong bond, a printers blanket made in accordance with the herein described procedure has materially better wearing'qualities than those made by processes derivable from prior art treatments. A printer's blanket made according to the present invention has a further advantage over those of the prior art in that the improved coating composition for the impregnated felt is dry, flexible, non-tacky and highly resistant to cracking and peeling when subjected to repeated high pressure.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to finedin the appended claims.

I claim:

1. A resilient printers blanket which comprises a woven felt fabric deeply impregnated by small particles of cellulose nitrate and a flexible plasticizer and an outer part containing an inkrepellent material.

2. A resilient printers blanket which comprises a woven woolen felt fabric deeply impregnated with small particles of cellulose nitrate, and bonded thereto an inner layer of plasticizer free cellulose nitrate, an'intermediate layer of cellulose nitrate containing a castor oil modified polyhydric alcohol straight chain dibasic acid resinous product and an outer layer of cellulose nitrate containing aluminum bronze.

3. A felt impregnated with an oil in water type cellulose derivative emulsion, an intermediate coat of plasticizer free cellulose nitrate and finally coated with a composition consisting of- Mill base: Per cent Lithopone per cent 36.10 Yellow ochre do 12.04 Boneblack do 6.26 A 60 per cent solution in toluol 12 1 of castor oil modified polyhydric alcohol straight chain dibasic acid resinous product per cent 45.60 24 ounce cellulose nitrate solution (24 ounces C, N. for each gallon of solvent) in 60-40 ethyl alcohol-ethyl acetate (1 .44% C. N; by weight) 50.4 A 60 per cent solution in toluol of a castor oil modified polyhydric alcohol straight chain dibasic acid resinous product 17.1 Ethyl alcohol 12.2 Ethyl acetate 8.2

RAYMOND E. THOMAS. 

